1. Field of the Invention
This invention relats to a rust preventive coating composition, and more particularly to the rust preventive coating composition suitable for being applied onto the underfloor of a motor vehicle such as an automotive vehicle.
2. Description of the Prior Art
Hitherto application of rust preventive coating has been extensively carried out for the underfloor of automotive vehicles in order to protect the underfloor from production of rust and corrosion. Examples of the rust preventive coating are so-called underfloor wax having a solid content of about 30 wt%, and so-called bitumen wax having a solid content of about 60 wt%. The underfloor wax consists of 10 wt% of metallic salt of sulfonic acid, 10 wt% of metallic salt of petrolatum oxide, 7 wt% of microcrystalline wax, 7 wt% of paraffin synthetic oil, 0.1 wt% of carbon black and 65.9 wt% of mineral spirit. The bitumen wax consists of 13 wt% of asphalt, 13 wt% of microwax, 10 wt% of metallic salt of sulfonic acid, 8 wt% of metallic salt of lanolin fatty acid, 15 wt% of calcium carbonate and 41 wt% of mineral spirit. The underfloor wax is usually applied onto the underfloor which requires a relatively thin rust preventive film. The bitumen wax is usually applied onto the underfloor which requires a relatively thick rust preventive film.
However, if the underfloor wax is applied thick to form a thick rust preventive film, running of the wax tends to occur during application of the wax, so that it is impossible to form the rust preventive film having a thickness of 300 .mu.m. Additionally, in this case, the underfloor wax is difficult to be dried and therefore is deteriorated in operation efficiency. If the bitumen wax is applied thin to form a thin rust preventive coating film, lack of binding and nonuniformity of the rust preventive film are made thereby to render impossible to form a uniform rust preventive film on the underfloor of the automotive vehicle. Furthermore, the solid contents of the underfloor wax and the bitumen wax cannot be increased to levels of about 30 wt% and about 60 wt%, respectively, from the standpoint of maintaining necessary coating efficiency, and therefore a larger amount of organic solvent (mineral spirit) affecting human body is unavoidably contained in these waxes.